Mahé, K.

Songer, S.

Zenner, A.

Open Marine Archive

ICES WKNARC REPORT 2011 |  23 
 
• There are several age readers for each stock/species and bilateral agree-
ments exist with age readers at other institutes who read CS from the same 
stock/species. CS preparation and age reading procedures and manuals ex-
ist for all stocks/species. Reference collections are used for each 
stock/species and these are updated at intervals with new CS, to reduce the 
possibility of unintentional bias caused by too frequent exposure to the 
same CS or (CS image). There are regular scheduled exercises to monitor 
changes in the age reader performance. There are specified training pro-
grammes that require the trainee to be closely supervised for a period of 
time, before they can enter the cycle of quality management for age readers 
who contribute data to assessments. A quality manual exists and this de-
fines how reference collections are managed, how training programmes 
are managed and how quality checks and controls are carried out. The age 
readers take part in all relevant age calibration exchanges (EX) and age 
calibration workshops (WKAC). This is the most preferable level of inter-
nal quality management. Original CS are catalogued and stored in a way 
that will prevent damage, loss or deterioration. The reference collections 
are managed using an image database (N.B. WebGR can be installed lo-
cally for this purpose). The management of all documents is controlled and 
is properly managed, typically by means of an electronic document reposi-
tory. Unauthorised changes to quality documents are not permitted and 
printed versions will be watermarked as uncontrolled documents. It is 
likely that Institutes that meet these requirements may have, or be capable 
of obtaining quality management certification, e.g. ISO 9001: 2008 and ISO 
17025 (accreditation). 
7.2 External Quality Management 
Accreditation is the highest level of external quality management and two MS insti-
tutes currently hold national accreditation, CEFAS (ISO 17025 - UKAS) and IVLO 
(ISO 17025 - BELAC). 
7.3 Study on Harmonised methodology of age estimation Procedures 
Most of European fish stocks are assessed using age-based models. In this context, 
the quality of these data plays a vital role in management of fish resources. Errors in 
age estimation can be caused by accuracy and/or precision issues (Campana, 2001) 
and they have to be detected and quantified. Accuracy refers to the closeness be-
tween measurements and their true value. Precision is defined as the variability in 
the age readings. Within and between age reading laboratories there will inevitably 
be disagreements between age readers.  
The European Commission supported the development of a European Fish Ageing 
Network with two Concerted Actions, i.e. EFAN (European Fish Aging Network) 
and TACADAR (Towards Accreditation and Certification of Age Determination of 
Aquatic Resources) from 1997 to 2006. The overall theme of both CAs was to harmo-
nise the fish age estimation, mostly carried out by interpreting calcified structures. 
Since 2006, the ICES Planning Group on Commercial Catch, Discards and Biological 
Sampling (PGCCDBS) organises each year of calibration exercises and workshops on 
calcified structures to estimate precision and relative/absolute bias in the age estima-
tions from readers based in different ageing laboratories. 
24  | ICES WKNARC REPORT 2011 
 
In 2007, the PGCCDBS meeting decided to produce the first international age length 
key (ALK) for the sole in the Eastern English Channel (ICES area VIId) in 2008. In the 
future, the international ALK should develop requiring the harmonisation of the age 
estimation procedures. 
Proposition:  
The objective for this proposal is to develop a harmonised methodology and quality 
assurance process for age estimation procedures for a small region with a group of 
countries, before trying to achieve general harmonisation of these procedures for all 
ICES areas. Firstly, we need to identify the region and common species/stocks to be 
used in this trial harmonisation. The techniques for each step from sampling of the 
calcified pieces to the storage/archiving then need to be described and compared per 
country and per species/stocks. Common tools for quality indication and assurance 
need to be developed for each step of the age estimation procedure. The most qualita-
tive procedures will then be used for optimisation and harmonisation of the protocols 
(methods of preparation, material etc.) per species/stock and among species/stocks. 
This will then result in a harmonised quality control mechanism and the develop-
ment of guidelines for good techniques and good operating procedures. According to 
these harmonised protocols, we will also need to develop consistent training for new 
age readers (per species/stock). These new sets of harmonised protocols will give 
more strength for accreditation processes and will strengthen already accredited labs. 
This study was presented during the Regional Coordination Meeting for the North 
Atlantic (RCM NA) 2010 and during the ICES Planning Group on Commercial Catch, 
Discards and Biological Sampling (PGCCDBS) 2011 meeting. 
WKNARC is supporting the idea of this study with a small number of case studies. 
7.4 Proposal for the use of a standard grading system by age readers of 
their own readings to register the confidence level the reader has in 
their otolith readings, reflecting the quality of the data. 
PGCCDBS recommends the use of a standard grading system by the mackerel age 
reader of his/her own readings (e.g. high, medium, low) be considered during the 
WKNARC as a standard that could be applied in all age calibration ex-changes 
and/or WKs (ref. WKARMAC 2010).  
It is a recommendation of the WKARMAC 2010 Workshop to register the confidence 
level the reader has in their otolith reading, reflecting the quality of the data. Most 
readers should use a scale of 3 levels of quality:  
• Rings can be counted with certainty: 1  
• Rings can be counted, but with difficulty and some doubt: 2  
• Rings cannot be counted, the otolith is unreadable: 3  
WKNARC supports the PGCCDBS recommendation for the use of a grading system 
by the age reader of their own readings in all age calibration exchanges and/or WKs. 
Reading the ages of calcified structures is a subjective process, where the reader uses 
their acquired knowledge of CS growth zone patterns and the biology of a species-
stock, to estimate the age of individual CS that are believed to be from that species-
stock. Typically, age readers who provide the age data that are used in stock assess-
ments are experienced in reading the CS of the species-stocks studied at their insti-
tutes. Several different scales of different lengths have been used at MS institutes and 


Study on Harmonised methodology of age estimation Procedures

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